This application claims the benefit of Japanese Patent Application Number 2006-53637 filed on Feb. 28, 2006, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a dust prevention mechanism for preventing a state where ambient air including cutting liquid or cutting chips enters an inner portion of a spindle device which is installed in a machine tool, for example.
2. Description of the Related Art
Generally, a spindle device installed in a machine tool and so on, is used in an atmosphere where cutting liquid and cutting chips and the like are mixed. When the cutting liquid and the cutting chips and the like enter an inner portion of the spindle device (for example, a gear portion or a bearing), there are problems in the spindle device, and the life of the spindle device would be shortened. In particular, the problems are serious when a spindle of the spindle device, which is rotating in a high speed, is stopped or the rotational speed of the spindle is drastically reduced. When the spindle rotates in a high speed, air in the inner portion of the spindle device flows outside since the air expands due to the heated inner portion. In this state, upon stop of rotation of the spindle, ambient air including cutting liquid or cutting chips enters the inner portion of the spindle device during drop of the temperature of the inner portion of the spindle device. Therefore, in order to protect the spindle device from this situation, that is, to prevent the ambient air from entering the inner portion of the spindle device, dust prevention mechanisms as disclosed in patent documents 1 and 2 are devised.
[Patent document 1] Japanese patent publication of unexamined application No. 5-261603
[Patent document 2] Japanese patent publication of examined application No. 8-22494
Here, the dust prevention mechanisms disclosed in the patent documents 1 and 2 will be explained.
The dust prevention mechanism in the patent document 1 includes an air vent with a relatively large diameter defined on a spindle casing. The air vent actively allows ventilation of ambient air between the inner side and the outer side of the spindle casing, which inhibits increase of pressure in an inner portion of the spindle casing when a spindle in the spindle casing rotates in a high speed. As a result, an amount of the ambient air entering the inner portion of the spindle casing is reduced upon stop of rotation of the spindle.
The dust prevention mechanism in the patent document 2 includes a pressure detection sensor attached in an inner portion of a spindle device (for example, a labyrinth portion). In the inner portion of the spindle device, compressed fluid such as compressed air is supplied so as to maintain positive pressure.
However, since the dust prevention mechanism in the patent document 1 actively allows ventilation of ambient air between the inner side and the outer side of the spindle device, it is difficult to prevent cutting liquid or cutting chips and the like from entering the inner portion of the spindle device even though the amount of the ambient air is reduced as much as possible. Therefore, the problem that the life of the spindle device is shortened has not been resolved effectively.
The dust prevention mechanism in the patent document 2 requires the pressure detection sensor attached in the inner portion of the spindle device, and inner pressure of the spindle device has to be constantly detected to compare the inner pressure with outer pressure using the pressure detection sensor. As a result, costs of the mechanism will be increased. Furthermore, the compressed fluid is supplied regardless of a state of the spindle device, for example, rotation of a spindle of the spindle device and rotational speed of the spindle. Consequently, an excessive amount of the compressed fluid will be supplied, which is a waste of the compressed fluid.
In order to solve the above problems, the present invention is made to provide a dust prevention mechanism of a spindle device that ensures prevention of cutting liquid etc. from entering the inner portion of the spindle device, which saves energy and reduces noise upon stop of rotation of the spindle.